In the past, a charging device for charging the surface of a photoreceptor (image bearing member) in an electrophotographic image forming apparatus was a corona charger which generates a large amount of ozone. In recent years, however, a contact roller charger which generates a small amount of ozone has been used due to environmental concerns. In addition, a high-speed apparatus (image forming apparatus capable of high-speed processing) including the contact roller charger has been developed.
In the electrophotographic image forming apparatus, part of a toner of a toner image formed on the photoreceptor is transferred to an intermediate transfer body or a transfer medium, such as a transfer sheet, in the transfer process, while the rest of the toner remains on the surface of the photoreceptor even after the transfer process. The remaining toner left on the photoreceptor results in a low image quality in the subsequent image formation. In order to remove the residual toner on the photoreceptor, a cleaning device provided with a cleaning blade that is brought into contact with the photoreceptor is frequently used. In the transfer process, a rate of transfer of a toner to the transfer medium is approximately 95% at the highest. Therefore, some of the toner remains on a photoreceptor drum (such toner is referred to as “residual toner”). The residual toner is basically all cleaned in the cleaning process that follows the transfer process.
However, as described above, in a normal cleaning device of the electrophotographic image forming apparatus is adopted a blade cleaning system that realizes a simple structure and easy control. During the cleaning in the blade cleaning system, a certain degree of vibration occurs in the photoreceptor and the cleaning blade at the micro level (slip-stick phenomenon). Because of this, the residual toner can pass through the cleaning blade at some timing.
Here, in a case where the contact roller charger is used as a charging device, incomplete cleaning with a cleaning blade causes the following event. That is, toner and silica additive of small-diameter particles passing through the cleaning blade contaminate the charging roller. As a result of this, phenomena such as charging performance deterioration and uneven charging occur. These phenomena are more likely to occur especially in high-speed apparatuses.
As a solution for such a problem, there has been studied a method in which a cleaning section such as a sponge roller or a cleaning brush is brought into contact with a charging roller to perform cleaning. For example, Patent Document 1 (Japanese Unexamined Patent Publication No. 66807/2003 (Tokukai 2003-66807; published on Mar. 5, 2003) discloses a transferring device and a charging device which includes a cleaning member that is formed with a melamine resin foam at a part where it comes into contact with an object to be cleaned. Further, for example, Patent Document 2 (Japanese Unexamined Patent Publication No. 4749/2004 (Tokukai 2004-4749; published on Jan. 8, 2004) discloses an image forming apparatus having a cleaning section which comes into contact with a charging member to remove foreign substances adhered to the surface of the charging member.